The invention relates to a pump, particularly for washing machines, dishwashing machines and the like, having a housing and a heating device for the continuous heating of a liquid, particularly water, in which the heating device is constructed as the circumferential wall of the housing.
For heating the water necessary for operation, it is known to place in the interior of such devices heating elements such as heating coils. However, not only are the design and assembly costs also in conjunction with possible repairs, but also the direct contact of the heating elements with the water to be heated, which in particular with highly calcareous waters lead to significant reductions in the service life and efficiency of the heating coils are disadvantageous or can make necessary further constructional measures. Frequently mechanical damage occurs to the heating coils through dropping objects.
It is also known to position upstream of said devices a boiler or a separate hot-water heater, where the water is heated to the necessary temperature. However, such additional units require extra space, so that the devices either have larger dimensions or their useful volume is correspondingly reduced and are in part complicated from the design standpoint and correspondingly cost intensive.
It has finally been proposed to place a heating device on the outside of the sump container housing, but this does not lead to a uniform heating of the water.
DE 199 03 951 A1 describes a pump for washing machines, dishwashers, etc. having a housing and a heating device for continuous liquid heating, the latter having a heater located on the outside of the pump housing and a heat distributing plate positioned between the pump housing wall and the heating device for the uniform distribution of the heat produced by the heating device over the pump housing. Although this leads to a uniform heating of the water whilst avoiding the aforementioned disadvantages, it is disadvantageous in the case of the known pump that the entire pump housing is made from metal for thermal conductivity reasons and consequently requires relatively high material and manufacturing costs.
DE 197 36 794 C2 discloses a circulating pump for a dishwasher, where the pump housing is formed by heating coils embedded in a sleeve-like heater.
The upper end of the heater is circumferentially surrounded by a bearing stud of a bearing element for a spray arm, whereas the lower face terminates in free, spaced manner with respect to a bearing plate, through which only pass the heater connections. The overall construction is complicated and costly.
The problem of the invention is to propose a simple, inexpensive pump of the aforementioned type which, whilst avoiding the aforementioned disadvantages, ensures a uniform, continuous liquid heating.
According to the invention this problem is solved with a pump of the aforementioned type in that on one face of the heating device is placed in sealing manner a base and on another face of the heating device is placed in sealing manner a cover of the housing.
In the case of the pump according to the invention the heat supply consequently does not take place by indirect heating of the pump housing via heat distributing plates and instead the heating device forms part of the pump housing, whereas the remaining housing part constituted by the base and the cover is preferably made from plastic, which can be inexpensively obtained and in particular inexpensively processed. These housing parts can be made from random thermoplastic or thermosetting materials, such as polyolefins (polyethylene, polypropylene, etc.), polyamides, polyesters, polyacetates, polycarbonates, vinyl polymers, polyurethanes, etc. or from polymer blends, which have an adequate thermal stability for pump use.
In order to ensure a high efficiency of the heat transferred by the heating device to the liquid flowing through the pump, the heating device is appropriately located on an area of the housing where, for flow reasons, the formation of a temperature gradient in the liquid is avoided. The heating device is preferably located between a housing base and cover, so as to form a substantially annular housing circumferential wall. Thus, particularly with the centrifugal pumps used for liquid heating of washing machines, dishwashers, etc., where the liquid delivered by the pump passes over a circular path, it is ensured that the heat supply takes place in a high turbulence area of the liquid leading to a high heat transfer. Through the formation of an annular side wall a simply designed pump housing structure is obtained, the housing cover and housing base being made from plastic and the annular side wall can be e.g. separately manufactured.
In a preferred embodiment, the heating device has a metal ring forming at least part of the housing side wall, said ring preferably being made from high-grade steel, particularly high-grade sheet steel, or from aluminium. In the latter case the aluminium ring can e.g. be a casting or an extruded part and then the inside is coated. Alternatively the heating device can have a ring of heat conductive plastic forming at least part of the housing side wall. Then, in particular electrically conductive plastics can be provided.
Advantageously, for heating the ring forming the housing side wall, the heating device has a thick film resistor externally in contact with the ring or a tubular heater externally in contact with the ring, which is located around at least a partial circumference of the ring and consequently at least partly surrounds the same.
In the case of a heating device having a tubular heater, the ring advantageously has a corrugation at least partly receiving the tubular heater, so as on the one hand to securely and permanently fix the tubular heater to the outside of the ring and on the other so as to ensure an increased heat exchange surface between the tubular heater and the ring. Alternatively or additionally a heat distributing plate, preferably from aluminium, can be positioned between the ring and the tubular heater.
If the ring is made from an electrically conductive plastic, there is no need for the actual heating element, e.g. in the form of a tubular heater or thick film resistor and the plastic ring is then directly electrically heated.
Whereas in the case of a thermoplastic housing the ring can be directly injection moulded into the latter, when the housing is made from a thermosetting material it can be moulded into the housing. The ring can be bonded to the housing or, optionally accompanied by the interposing of seals, can be pressed with the housing.
In order to provide corrosion protection with aluminium rings, the pump heating device is preferably provided with a coating on the inside. It is also possible to provide temperature regulating devices in contact with the heating device in order to individually adjust the desired liquid temperature.
As stated, the pump is preferably a centrifugal pump.
In order to secure the connection of heating device and housing parts, according to a preferred development of the invention a retaining device embraces extensions of the housing parts. This reliably prevents any leaks of the connection, particularly if the heating element ring is a metal part and the remaining parts of the housing are made from plastic, because then as a result of the heating and cooling processes stresses can arise between the heating device and the plastic housing due to the different expansion coefficients of the materials and over a long period of time could lead to leaks at the connection. Moreover, within the pump, due to the liquid flow, an elevated pressure prevails all round, which on the one hand acts perpendicularly on the heating device and therefore presses the latter outwards and on the other the pressure also acts perpendicularly on the adjacent housing base and cover. Therefore the connection between the heating device and housing is burdened in two directions. These forces are also absorbed and compensated by the retaining device provided according to the invention. Moreover, through the use thereof the connections can be released non-destructively, i.e. a replacement of defective parts is possible. The retaining device can also be used for pressing an excess temperature protection means against the heating device, so that there is no need for an additional and separate fastening structure for the same.
Thus, this development provides for a fastening possibility reliably withstanding the internal pressure of the pump housing and rationally manufacturable in the form of the plastic housing and the heating device and which despite different expansion coefficients remains tight in the long term and in which an excess temperature protection means can be constructionally simply integrated. The overengaging retaining device can either be formed by the actual heating ring or by an additional connecting device. If the overengaging retaining device is formed by additional means, this offers the advantage that in the retaining device can simultaneously also be incorporated the fastening for the necessary excess temperature protection means.
The interposing of a seal has the advantage that the elasticity of said seal can compensate expansion coefficients and consequently creates a long term, tight connection. With the overengaging construction extensions are formed on the edges of the housing base and cover, which form the connection between the housing and the heating device and which receive the fastening structure on their side remote from the heating device and referred to here as the outside of the extension. This makes it possible to reliably counteract the pressure perpendicular to the housing base and cover. In addition, on the outside of the extension can be formed a groove, into which can, as desired, be clamped, pressed, crimped or snapped the connecting element and as a result the heating element is secured against the perpendicular pressure.
A particularly simple constructional solution arises if the overengaging connecting elements are constructed as clamps. The e.g. spring steel clamps are elastically preloaded at several points bilaterally snapping into the in this case not necessarily circumferential groove on the outside of the extension. On the inside of the extension is provided a circumferential, annular groove, which receives the heating device, accompanied by the interposing of a seal. Thus, in simple manner, a connection is created, which counteracts the lateral and also the vertical pressure on the heating element. When using clamps, the fitting of the excess temperature protection means can be especially advantageously implemented. In this case the excess temperature protection means is elastically clamped between the heating device and the clamp, optionally by means of a tongue bent out of the same.
Another possibility for creating a retaining device consists of the use of a plastic moulding, which can comprise several segments. Such a plastic moulding can be inexpensively manufactured as an injection moulding. At its ends are formed hook-like extensions engaging and hooking in identical, but opposing manner in the wall of an external groove of the plastic housing extension. Thus, a clip connection is produced through the elasticity of the plastic. The plastic connecting part is shaped in such a way that on the inside of the extension it simultaneously presses the heating device against the housing base and cover, accompanied by the interposing of a seal. Thus, here again the connecting part reliably absorbs in both directions the pressure on the heating device. On said retaining device can be shaped in simple manner a mounting support for the excess temperature protection means, so that the latter comes to rest between the retaining device and the heating device.
The segments can also be shaped in such a way that they externally completely embrace the heating device. Thus, the heating device is mechanically and electrically protected making a further housing part for protecting the heating device unnecessary.
Another simple fastening possibility is obtained through a ring of the heating device being used as an overembracing retaining device between the housing base and cover. To this end the cross-section of the ring is not planar and instead in its marginal areas and bilaterally is formed a U-shaped extension, which embraces in contour-adapted manner the plastic housing extension, accompanied by the interposing of a seal. For the final fastening the U-shaped extension of the heating device on the outside thereof is crimped or flanged into an external groove of the housing parts and is consequently secured against lateral and perpendicular pressure. With the aid of a simple clamp construction it is possible in this case to fix the excess temperature protection means to the heating element.